Light emitting diode light bar module with electrical connectors formed by injection molding

ABSTRACT

The present disclosure relates to methods for fabricating electrical connectors of a waterproof connector-heat sink assembly of a LED light bar module using injection molding. The methods include matching the coefficient of thermal expansion (CTE) of injection molding materials for the connectors and heat sinks. A heat sink and conductor pins are inserted into an injection mold and the injection molding materials are injected into the injection mold. An integrated connector-heat sink assembly is formed when the injection molding materials of the connectors form a waterproof seal with the heat sink when the injection molding materials solidify. Placement of the heat sink and conductor pins inside the injection mold is controlled to ensure that adhesive bonding between the injection molding materials and the heat sink is stronger than a maximum shear force.

BACKGROUND

Light emitting diode (LED) light bar modules enclose LEDs that emitlight when voltages are applied to the LEDs. LED light bar modules mayinclude a heat sink to aid in heat dissipation and connectors that areattached to the heat sink for supplying power and controls to the LEDs.LED light bar modules are frequently used in outdoor applications suchas street lighting and signage lighting. Thus, the connectors and heatsink are required to form a waterproof seal. To increase light output,two or more LED light bar modules may be connected in series through theconnectors of the LED light bar modules. However, when plugging orunplugging the connectors to connect or disconnect the LED light barmodules, the connectors and the attached heat sink are subject to ashear force. Thus, the connector-heat sink assembly is additionallyrequired to have a strength of adhesive bonding between the connectorsand the heat sink that is strong enough to withstand the expected shearforce. Conventionally, connectors are glued to heat sinks to achieve thewaterproof seal and the adhesive bonding when assembling the LED lightbar modules.

While methods of attaching connectors to heat sinks by gluing have beenwidely practiced, the performance of the connector-heat assemblies hasnot been entirely satisfactory. For example, environmental conditionssuch as changing temperatures and humidity may cause the glue in theconnector-heat assemblies to peel or chip, degrading the integrity ofthe waterproof seal and the adhesive bonding between the connectors andthe heat sinks. Furthermore, gluing connectors to heat sinks increasesmanufacturing complexity and cost for the LED light bar module assemblyprocess. Accordingly, there is a need for methods of fabricatingconnector-heat sink assemblies that are capable of maintainingwaterproof seal and adhesive bonding between connectors and heat sinksover environmental conditions while reducing manufacturing process andcost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a perspective view of an LED light bar module withinjection molded connectors according to one or more embodiments of thepresent disclosure.

FIG. 1B shows an exploded view of the LED light bar module of FIG. 1Aaccording to one or more embodiments of the present disclosure.

FIG. 2 shows a flowchart of a method for fabricating connectors of awaterproof connector-heat sink assembly of the LED light bar module ofFIG. 1A using an injection molding process according to one or moreembodiments of the present disclosure.

FIG. 3A shows a positioning of conductor pins relative to the heat sinkfor fabricating a male connector using the method of FIG.2 according toone or more embodiments of the present disclosure.

FIG. 3B shows a positioning of connector pins relative to the heat sinkfor fabricating a female connector using the method of FIG. 2 accordingto one or more embodiments of the present disclosure.

FIG. 4A shows a position of an injected molded male connector relativeto the heat sink fabricated using the method of FIG. 2 according to oneor more embodiments of the present disclosure.

FIG. 4B shows a position of an injected molded female connector relativeto the heat sink fabricated using the method of FIG. 2 according to oneor more embodiments of the present disclosure.

Embodiments of the present disclosure and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

The present disclosure relates to methods for fabricating electricalconnectors of a waterproof connector-heat sink assembly of a LED lightbar module using injection molding. The connector-heat sink assemblyincluding the injected molded connectors and the heat sink remainwaterproof over all operating conditions and a life cycle of the LEDlight bar module, and are also resistant to strong shear force. It isunderstood that the present disclosure provides many different forms andembodiments, and that specific embodiments are provided only asexamples. Further, the scope of the present disclosure will only bedefined by the appended claims. In the drawings, the sizes and relativesizes of regions may be exaggerated for clarity. It will be understoodthat when an element is referred to as being “on,” “connected to,” or“coupled to” another element, it may be directly on, connected to, orcoupled to the other element, or intervening elements may be present.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as being “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the exemplary term “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

Hereinafter, embodiments of the present disclosure will be explained indetail with reference to the accompanying drawings.

FIG. 1A shows a perspective view of an LED light bar module 100 withinjection molded connectors according to one or more embodiments of thepresent disclosure. The LED light bar module 100 includes a maleconnector 110 and a female connector 120 disposed on two opposite endsof a heat sink 130. Heat sink 130 has a channel running down itslongitudinal length with openings at the two opposite ends of thechannel for the connectors. In the present embodiment, male connector110 and female connector 120 are fabricated by an injection moldingprocess using polybutylene terephthalate (PBT) filled with 30% glassfiber as the injection molding materials. Alternative embodiments ofmaterials for the connectors include polycarbonate or other types ofplastic. Also in the present embodiment, heat sink 130 is made fromaluminum 6063-T5, an aluminum alloy. Alternative embodiments ofmaterials for heat sink 130 include other metals having good thermalconductivity. Heat sink 130 aids in the dissipation of heat generated byLEDs housed inside LED light module 100.

Male connector 110 and female connector 120 serve as an inlet and anoutlet for power and control signals to LED light bar module 100. Inaddition, two or more LED light bar modules 100 may be connected inseries by plugging male connector 110 of a first LED light bar module100 into female connector 120 of a second LED light bar module 100. Theserially connected array of LED light bar modules 100 is used inapplications requiring increased light output. Each LED light module 100thus receives its power from either male connector 110 or femaleconnector 120, and also passes power through the other connector to thenext LED light module 100 in series.

Male connector 110, female connector 120, and heat sink 130 form awaterproof connector-heat sink assembly to keep away moisture andcontaminants from the interior of LED light bar module 100. Thewaterproof seal is maintained over environmental conditions under whichLED light bar module 100 is expected to operate. For example, if LEDlight module 100 is used for street lighting, the connector-heat sinkassembly maintains the waterproof seal across variations in temperature,humidity, radiation, etc. under which the street lighting would operate.Thus, the PBT with 30% glass fiber of male connector 110 and femaleconnector 120, and the aluminum 6063-T5 of heat sink 130 are chosen tohave substantially the same coefficients of thermal expansion (CTE) tohelp maintain a waterproof seal across variations in environmentalconditions. In addition, male connector 110 and female connector 120need to adhere to heat sink 130 with an adhesive force that is strongenough to withstand a shear force the connector-heat sink assembly issubject to when one LED light bar modules 100 is plugged into orunplugged from another LED light bar module 100. Because the strength ofadhesive bonding between male connector 110 or female connector 120 andheat sink 130 is a function of the contact surface area, male connector110, female connector 120 are fabricated to have sufficient contactsurface areas with heat sink 110.

The connector-heat sink assembly is attached to a housing 140 that runslongitudinally above the connector-heat sink assembly. In the presentembodiment, housing 140 is glued to male connector 110, female connector120, and heat sink 130. Alternative embodiments of attaching housing 140to the connector-heat assembly include using screws. The connector-heatassembly and housing 140 enclose LEDs within LED light bar module 100.Housing 140 has an array of openings running longitudinally forplacement of an array of LED lens 150 through which the enclosed LEDsemit light. In the present embodiment, LED lens 150 is made of epoxy.LED lens 150 shapes an emitted light pattern from the LEDs when power isapplied to LED light bar module 100 through male connector 110 or femaleconnector 120.

FIG. 1B shows an exploded view of the LED light bar module of FIG. 1Aaccording to one or more embodiments of the present disclosure. Maleconnector 110, female connector 120, and heat sink 130 define aninterior cavity of LED light bar module 100 for placing an LED PCB(printed-circuit board) 160. LED PCB 160 contains circuitry for drivingthe array of LEDs placed on the upward facing surface of LED PCB 160.LED PCB 160 is attached to heat sink 130 to provide a thermal conductivepath through heat sink 130 for dissipating heat generated by the arrayof LEDs. In addition, LED PCB 160 connects to one of male connector 110or female connector 120 to receive power and control signals for thearray of LEDs. LED PCB 160 also connects to the other connector to passthe power and control signals to the next LED light bar module connectedin series. An array LED lens 150 is placed over the array of LEDs toshape emission patterns and optionally bandwidths of emitted light fromthe LEDs. Housing 140 containing the array of openings for the array ofLED lens 150 is attached over the top of LED light bar module 100.

FIG. 2 shows a flowchart of a method for fabricating connectors of thewaterproof connector-heat sink assembly of the LED light bar module ofFIG. 1A using an injection molding process according to one or moreembodiments of the present disclosure.

As discussed, the CTEs of materials used to fabricate male connector110, female connector 120, and heat sink 130 need to be substantiallythe same to help maintain a waterproof seal across variations inenvironmental conditions. In particular, as temperature changes, maleconnector 110, female connector 120, and heat sink 130 expand orcontract by substantially the same amount to help maintain the integrityof the waterproof seal.

In step 200, the CTE of heat sink 130 is determined when materials forheat sink 100 is chosen. In the present embodiment, aluminum 6063-T5 ischosen because it has good thermal conductivity, is lightweight, and hasa CTE that is readily matched by plastic materials used for theconnectors. For example, aluminum 6063-T5 has a CTE of 23.4 μm/m-° C.over a temperature range of 20-100° C.

In step 202, injection molding materials of the connectors are selected.Selection criteria for step 202 include, but are not limited to,materials that are suitable for the injection molding process, have goodmechanical property, and have a CTE that is substantially the same asthat of the heat sink material. In the present embodiment, PBT filledwith 30% glass fiber is selected because it is suitable for use as aninjection molding material, adheres to aluminum 6063-T5 of heat sink 100to form a tight seal, and has a CTE of 23.4-25.2 μm/m-° C. over atemperature range of 60-138° C. Alternative embodiments includepolycarbonate or other types of plastic materials.

In addition to the injection molding materials, male connector 110 andfemale connector 120 include connector pins to provide electricalconnections. The connector pins are surrounded radially by the injectionmolding material. Therefore, consideration is also given to the CTE ofthe connector pins when evaluating the waterproof seal of theconnector-heat sink assembly. However, due to the relatively smallcontact surface area between the connector pins and the injectionmolding materials, CTE matching between the connector pin and theinjection molding materials is not critical for maintaining theintegrity of the waterproof seal of the connectors. Therefore, there ismore flexibility in selecting materials for the conductor pins. In thepresent embodiment, metal pins are made of copper surrounded by gold fortheir good conductive property.

As discussed, the strength of adhesive bonding between two surfaces is afunction of the contact surface area between the two surfaces. Inparticular, the strength of adhesive bonding between male connector 110or female connector 120 and heat sink 130 is a product of their contactsurface area multiplied by the strength of adhesive bonding per unitarea between the materials of male connector 110 or female connector 120and heat sink 130. In addition, for the connector-heat sink assembly towithstand a maximum shear force when another connector is plugged intoor unplugged from the connector-heat sink assembly, the strength ofadhesive bonding between male connector 110 or female connector 120 andheat sink 130 has to be greater than the maximum shear force. Therefore,the contact surface area between male connector 110 or female connector120 and heat sink 130 has to be sufficiently large to produce therequired adhesive bonding strength. Similarly, the contact surface areabetween the conductor pins and male connector 110 or female connector120 has to be sufficiently large.

In step 204, the strength of adhesive bonding per unit area, T1, betweenthe selected injection molding material and heat sink 130 is determined.In the present embodiment, T1 is determined by running finite-elementsimulation of adhesive bonding between PBT filled with 30% glass fiberand aluminum 6063-T5. Alternative embodiments include conducting shearstress test on a connector-heat sink assembly having a known contactsurface area to determine the minimum shear force necessary to break theadhesive bonding between the connector and the heat sink.

In step 206, the maximum shear force, T1, that the adhesive bondingbetween the selected injection molding material and heat sink 130 needsto withstand is determined. As discussed, the strength of adhesivebonding between the selected injection material of male connector 110 orfemale connector 120 and heat sink 130 has to be greater than T1 tomaintain the integrity of the connector-heat sink assembly when T1 isapplied.

In step 208, the length, L1, of the contact surface area between maleconnector 110 or female connector 120 and heat sink 130 is determined.L1 determines the minimum length by which connector 110 or femaleconnector 120 makes contact with heat sink 130 in the longitudinaldirection. L1 is determined by first dividing the maximum shear force T1by τ1 to calculate the minimum required contact surface area betweenconnector 110 or female connector 120 and heat sink 130. Connector 110or female connector 120 makes contact with heat sink 130 along both thelongitudinal direction of heat sink 130 and along a cross section of thechannel of heat sink 130. Accordingly, the total contact surface areabetween connector 110 or female connector 120 and heat sink 130 is theproduct of the contact length in the longitudinal direction and c1, across sectional perimeter of the channel of heat sink 130. Therefore,once the minimum required contact surface area is determined, L1 iscalculated by dividing the minimum required contact surface area by c1.The calculation for L1 may be expressed as:

L1=T1/(τ1×c1)

Similarly, in step 210, the strength of adhesive bonding per unit area,τT2, between the selected injection molding material and the conductorpins is determined. In the present embodiment, τ2 is determined byrunning finite-element simulation of adhesive bonding between PBT filledwith 30% glass fiber and copper/gold. Alternative embodiments includeconducting shear stress test on a connector having a known contactsurface area between the injection molding material and the conductorpins to determine the minimum shear force necessary to break theadhesive bonding between the injection molding material and theconductor pins.

In step 212, the maximum shear force, T2, that the adhesive bondingbetween the selected injection molding material and the conductor pinsneeds to withstand is determined. The strength of adhesive bondingbetween the selected injection material of male connector 110 or femaleconnector 120 and the conductor pins has to be greater than T2 tomaintain the integrity of the connector when T2 is applied.

In step 214, the length, L2, of the contact surface area between theinjection molding material of male connector 110 or female connector 120and the conductor pins is determined. L2 determines the minimum lengthby which the conductor pins are seated in connector 110 or femaleconnector 120 in the longitudinal direction of the connectors. L2 isdetermined by first dividing the maximum shear force T2 by τ2 tocalculate the minimum required contact surface area between theinjection molding material of connector 110 or female connector 120 andthe conductor pins. Because the conductor pins are surrounded radiallyby the injection molding material, the total contact surface areabetween the conductor pins and the surrounding injection moldingmaterial is the product of the contact length in the longitudinaldirection and a total circumference, c2, of the conductor pins.Therefore, once the minimum required contact surface area is determined,L2 is calculated by dividing the minimum required contact surface areaby c2. The calculation for L2 may be expressed as:

L2=T2/(τ2×c2).

In step 216, a determination is made whether male connector 110 orfemale connector 120 is to be fabricated. If male connector 110 is to befabricated, in step 218, an opening of the channel of heat sink 130 isplaced inside an injection mold and positioned such that after theconnector is fabricated by the injection molding process, the injectionmolding material of male connector 110 will contact the channel of heatsink 130 by a length of L1 in the longitudinal direction. In the presentembodiment, the total longitudinal length of the injection moldingmaterial of male connector 110 is longer than L1 so that male connector110 protrudes out of the edge of heat sink 130 through the opening ofthe channel.

In step 220, conductor pins for male connector 110 are clamped andpositioned inside the injection mold to protrude from the edge of heatsink 130 through the opening of the channel. After male connector 110 isfabricated by the injection molding process, conductor pins will beseated in the injection molding material of male connector 110 by alength of L2 in the longitudinal direction.

If female connector 120 is to be fabricated, in step 222, an opening ofthe channel of heat sink 130 is similarly placed inside an injectionmold and positioned such that after the connector is fabricated by theinjection molding process, the injection molding material of femaleconnector 120 will contact the channel of heat sink 130 by a length ofL1 in the longitudinal direction. In the present embodiment, the totallongitudinal length of the injection molding material of femaleconnector 120 is L1. Therefore, female connector 120 will be recessedcompletely inside heat sink 130 with the edge of the injection moldingmaterial being coplanar with the edge of heat sink 130.

In step 224, connector pins for female connector 120 are clamped andpositioned inside the injection mold to be recessed from the edge ofheat sink 130. After female connector 120 is fabricated by the injectionmolding process, conductor pins will be seated in the injection moldingmaterial of female connector 120 by a length of L2 in the longitudinaldirection.

FIG. 3A shows a positioning of conductor pins 300 relative to heat sink130 for fabricating a male connector 110 using the method of FIG. 2according to one or more embodiments of the present disclosure. Asexplained in step 220, conductor pins 300 are positioned to protrudefrom the edge of heat sink 130 through the opening of the channel.

FIG. 3B shows a positioning of connector pins 300 relative to heat sink130 for fabricating a female connector 120 using the method of FIG. 2according to one or more embodiments of the present disclosure. Asexplained in step 240, conductor pins 300 are positioned to be recessedfrom the edge of heat sink 130.

Returning to FIG. 2, in step 226, a molten state of the injectionmolding material selected in step 202 is injected into the injectionmold in an injection molding process to fabricate male connector 110 orfemale connector 120. Alternative embodiments include using an injectionmold to fabricate both male connector 110 and female connector 120 in asingle injection process. In the present embodiment, PBT with 30% glassfiber is injected into the injection mold under a processing temperatureof between 180 and 200 degrees Celsius.

FIG. 4A shows a position of an injected molded male connector 110relative to heat sink 130 fabricated using the method of FIG. 2according to one or more embodiments of the present disclosure. Maleconnector 110 includes injection molding material 320 and conductor pins300. Injection molding material 320 protrudes out of the edge of heatsink 130 through the opening of the channel. Injection molding material320 also contacts the channel of heat sink 130 by a length of L1 in thelongitudinal direction. Conductor pins 300 also protrude from the edgeof heat sink 130 through the opening of the channel and are seated ininjection molding material 320 by a length of L2 in the longitudinaldirection.

FIG. 4B shows a position of an injected molded female connector 120relative to heat sink 130 fabricated using the method of FIG. 2according to one or more embodiments of the present disclosure. Femaleconnector 120 also includes injection molding material 320 and conductorpins 300. Injection molding material 320 of longitudinal length L1 isrecessed completely inside heat sink 130 with the edge of the injectionmolding material 320 being coplanar with the edge of heat sink 130. Inaddition, conductor pins 300 are recessed from the edge of heat sink 130and are seated in injection molding material 320 by a length of L2 inthe longitudinal direction.

Returning to FIG. 2, in step 228, the integrated connector-heat sinkassembly including male connector 110, female connector 120, and heatsink 130 is removed from the injection mold. In step 230, LED PCB 160containing an array of LEDs is placed inside the cavity of theconnector-heat sink assembly. LED PCB 160 is also connected to maleconnector 110 and female connector 120 to receive power and controlsignals for the array of LEDs. An array of LED lens 150 is secured overthe array of LEDs to shape emission patterns and optionally bandwidthsof emitted light from the LEDs. In step 232, housing 140 containing anarray of openings for array of LED lens 150 is attached over the top toenclose LED light bar module 100.

In accordance with one or more embodiments of the present disclosure, amethod for forming an electrical connector of an LED light bar module isdisclosed. The method includes determining the coefficient of thermalexpansion (CTE) of materials of a heat sink. The heat sink has a channelwith an opening. The method also includes selecting injection moldingmaterials to have a CTE that is substantially the same as the CTE of theheat sink materials. The method further includes placing the opening ofthe heat sink channel into an injection mold. The method furtherincludes clamping conductor pins into the injection mold at the openingof the heat sink channel. The method further includes injecting theinjection molding materials in molten state into the injection mold tofill cavities between the conductor pins and the heat sink. The methodfurther includes allowing the injection molding materials to solidifyinside the injection mold to form the electrical connector. Theelectrical connector includes the injection molding materials and theconductor pins that are surrounded radially by the injection moldingmaterials. The method further includes removing the electrical connectorand the heat sink from the injection mold.

In accordance with one or more embodiments of the present disclosure, amethod for forming an electrical connector of an LED light bar module isdisclosed. The method includes selecting a heat sink. The heat sink hasa channel with an opening. The method also includes selecting injectionmolding materials that are waterproof. The method further includesplacing the opening of the heat sink channel into an injection mold. Themethod further includes clamping conductor pins into the injection moldat the opening of the heat sink channel. The method further includesinjecting the injection molding materials in molten state into theinjection mold to fill cavities between the conductor pins and the heatsink to form the electrical connector. The electrical connector includesthe injection molding materials and the conductor pins that aresurrounded radially by the injection molding materials. The methodfurther includes forming a waterproof seal between the injection moldingmaterials and the heat sink channel by allowing the injection moldingmaterials to solidify. The method further includes removing theelectrical connector and the heat sink from the injection mold.

In accordance with one or more embodiments of the present disclosure, aconnector-heat sink apparatus of a light emitting diode (LED) light barmodule is disclosed. The apparatus includes a heat sink. The heat sinkhas a channel with an opening. The apparatus also includes a connectorplaced in the heat sink channel to form a waterproof seal with the heatsink channel. The connector includes injection molding materials and aset of conductor pins surrounded radially by the injection moldingmaterials. The connector is formed by an injection molding process.

Although embodiments of the present disclosure have been described,these embodiments illustrate but do not limit the disclosure. It shouldalso be understood that embodiments of the present disclosure should notbe limited to these embodiments but that numerous modifications andvariations may be made by one of ordinary skill in the art in accordancewith the principles of the present disclosure and be included within thespirit and scope of the present disclosure as hereinafter claimed.

1. A method of forming an electrical connector of a light emitting diode (LED) light bar module comprising: determining a coefficient of thermal expansion (CTE) of materials of a heat sink, wherein the heat sink has a channel with an opening; selecting injection molding materials having a CTE that is substantially the same as the CTE of materials of the heat sink; placing the opening of the channel of the heat sink into an injection mold; clamping a set of conductor pins into the injection mold at the opening of the channel of the heat sink; injecting the injection molding materials in molten state into the injection mold to fill cavities between the set of conductor pins and the heat sink; allowing the injection molding materials to solidify inside the injection mold to form the electrical connector, wherein the electrical connector includes the injection molding materials and the set of conductor pins surrounded radially by the injection molding materials; and removing the electrical connector and the heat sink from the injection mold.
 2. The method of claim 1, wherein the electrical connector comprises a male connector, wherein the male connector protrudes from the opening of the channel of the heat sink.
 3. The method of claim 1, wherein the electrical connector comprises a female connector, wherein the female connector is recessed from the opening of the channel of the heat sink.
 4. The method of claim 1, wherein the materials of the heat sink are aluminum 6063, and the injection molding materials are polybutylene terephthalate (PBT) filled with 30% glass fiber.
 5. The method of claim 1, wherein said placing the opening of the channel of the heat sink into an injection mold includes positioning the heat sink such that the injection molding materials will contact the channel of the heat sink by a length L1, and wherein said clamping a set of conductor pins into the injection mold includes positioning the set of conductor pins such that the set of conductor pins will be seated in the injection molding materials by a length L2.
 6. The method of claim 5, wherein L1=T1/(τ1×c1) and L2=T2/(τ2×c2), wherein: T1 is a maximum shear force between the injection molding materials and the heat sink; τ1 is a strength of adhesive bonding per unit area between the injection molding materials and the channel of the heat sink; c1 is a cross sectional perimeter of the channel of the heat sink; T2 is a maximum shear force between the injection molding materials and the set of conductor pins; τ2 is a strength of adhesive bonding per unit area between the injection molding materials and the set of conductor pins; and c2 is a total radial circumference of the set of conductor pins.
 7. The method of claim 5, wherein the electrical connector comprises a male connector, wherein the injection molding materials and the set of conductor pins protrude from the opening of the channel of the heat sink.
 8. The method of claim 5, wherein the electrical connector comprises a female connector, wherein an edge of the injection molding materials is coplanar with an edge of the opening of the channel of the heat sink, and the set of conductor pins is recessed from the edge of the opening of the channel of the heat sink.
 9. A method of forming an electrical connector of a light emitting diode (LED) light bar module comprising: selecting a heat sink, wherein the heat sink has a channel with an opening; selecting injection molding materials, wherein the injection molding materials are waterproof; placing the opening of the channel of the heat sink into an injection mold; clamping a set of conductor pins into the injection mold at the opening of the channel of the heat sink; injecting the injection molding materials in molten state into the injection mold to fill cavities between the set of conductor pins and the heat sink to form the electrical connector, wherein the electrical connector includes the injection molding materials and the set of conductor pins surrounded radially by the injection molding materials; forming a waterproof seal between the injection molding materials and the channel of the heat sink by allowing the injection molding materials to solidify; and removing the electrical connector and the heat sink from the injection mold.
 10. The method of claim 9, wherein the electrical connector comprises a male connector, wherein the male connector protrudes from the opening of the channel of the heat sink.
 11. The method of claim 9, wherein the electrical connector comprises a female connector, wherein the female connector is recessed from the opening of the channel of the heat sink.
 12. The method of claim 9, wherein the materials of the heat sink are aluminum 6063, and the injection molding materials are polybutylene terephthalate (PBT) filled with 30% glass fiber.
 13. The method of claim 9, wherein said placing the opening of the channel of the heat sink into an injection mold includes positioning the heat sink such that the injection molding materials will contact the channel of the heat sink by a length L1, and wherein said clamping a set of conductor pins into the injection mold includes positioning the set of conductor pins such that the set of conductor pins will be seated in the injection molding materials by a length L2.
 14. The method of claim 13, wherein L1=T1/(τ1×c1) and L2=T2/(τ2×c2), wherein: T1 is a maximum shear force between the injection molding materials and the heat sink; τ1 is a strength of adhesive bonding per unit area between the injection molding materials and the channel of the heat sink; c1 is a cross sectional perimeter of the channel of the heat sink; T2 is a maximum shear force between the injection molding materials and the set of conductor pins; τ2 is a strength of adhesive bonding per unit area between the injection molding materials and the set of conductor pins; and c2 is a total radial circumference of the set of conductor pins.
 15. The method of claim 13, wherein the electrical connector comprises a male connector, wherein the injection molding materials and the set of conductor pins protrude from the opening of the channel of the heat sink.
 16. The method of claim 13, wherein the electrical connector comprises a female connector, wherein an edge of the injection molding materials is coplanar with an edge of the opening of the channel of the heat sink, and the set of conductor pins is recessed from the edge of the opening of the channel of the heat sink.
 17. A connector-heat sink apparatus of a light emitting diode (LED) light bar module comprising: a heat sink having a channel with an opening; and a connector disposed in the opening of the channel to form a waterproof seal with the channel of the heat sink, wherein the connector includes injection molding materials and a set of conductor pins surrounded radially by the injection molding materials, and wherein the connector is formed by an injection molding process.
 18. The connector-heat sink apparatus of claim 17, wherein the injection molding materials have a coefficient of thermal expansion (CTE) that is substantially the same as the CTE of the heat sink.
 19. The connector-heat sink apparatus of claim 17, wherein the injection molding materials are polybutylene terephthalate (PBT) filled with 30% glass fiber and the heat sink is made from aluminum
 6063. 20. The connector-heat sink apparatus of claim 17, wherein a product of a contact surface area between the injection molding materials and the channel of the heat sink multiplied by a strength of adhesive bonding per unit area between the injection molding materials and the channel of the heat sink is greater than a maximum shear force that the connector-heat sink apparatus needs to withstand. 